The present invention relates to the production of carbon dioxide from a subterranean formation and more particularly relates to the production of carbon dioxide from a subterranean formation so that it will arrive at the surface in a single, supercritical phase.
It has long been recognized that carbon dioxide may be injected into an oil-bearing formation during a secondary or tertiary enhanced recovery operation to produce additional amounts of oil. One of the most attractive sources for carbon dioxide for this purpose is natural subterranean formations which produce large volumes of almost pure carbon dioxide. Unfortunately, many of the known formations capable of producing carbon dioxide in quantities sufficient for enhanced oil recovery operations are located several hundred miles from the oil fields in which the carbon dioxide is to be used. Accordingly, the carbon dioxide must be gathered from the carbon dioxide producing wells, treated, and then pipelined the several hundred miles to its final destination.
Due to the physical properties of carbon dioxide, it normally arrives at the surface from a production well in a two-phase state. As is known, flowing such a two-phase fluid through a pipeline over long distances of varying elevations creates a fluid "hammer" effect which is likely to cause serious damage to the pipeline and related equipment as well as considerable loss of horsepower. Therefore, the carbon dioxide has to be gathered and processed at or near the production wells and delivered to the pipeline as a single phase fluid, either gas, liquid, or supercritical fluid.
To do this, it has been proposed to position a central processing and compression station near several producing wells wherein the carbon dioxide from the well is heated, treated, and compressed for entry into the main pipeline. However, since a central processing and compression station will normally have to be located up to ten miles from some of the producing wells, a problem still exists in flowing the normally two-phase carbon dioxide from a production well to the central station through a gathering line, especially if the gathering line runs over hilly terrain.
At present, two known proposals have been made for gathering carbon dioxide from production wells and flowing it to a central processing station. First, if the production rates of carbon dioxide from a well are relatively small, small diameter flowlines, e.g., 3-inch, may be used as gathering lines so that any "hammer" effect caused by two-phase flow can be tolerated. Second, if production rates are large, thereby requiring large diameter, e.g., 10-inch, gathering lines, line heaters are to be provided at each producing wellhead to heat the produced carbon dioxide to thereby convert the liquid phase of the carbon dioxide into vapor before the carbon dioxide is delivered into the gathering line.
In the latter proposal, however, the amount of fuel needed to operate the line heater will be substantial and in addition to the costs involved, the actual logistics required to maintain a ready supply of fuel to the well sites at remote locations will present real problems.